This article will contain information on bushing insulators, their types and types. The design of various species, the species themselves, their scope and purpose will be analyzed in detail. Their advantages in comparison with similar devices will also be considered. After reading the article, you will not only learn general information about bushing insulators, but you will also be able to decipher the markings and be able to distinguish one species from another.
Scope of bushings
What is a bushing insulator? This is a special device whose main function is to insulate the conductive elements from the inner or outer wall of the shell through which they pass. They are also used when installing switchgears at transformer substations, also act as conclusions on complete switchgears.
Support insulators are designed to fix overhead power lines to live busbars of switchgears and other electrical installations. It is worth adding that porcelain insulators of the through type, which were popular earlier, are used to this day with many modifications.
Bushing insulators are very convenient to use for connecting the outputs of substations, from which residential buildings are powered.
Types of Insulators
Bushing insulators are divided into two types. The first type is insulators, which are designed for indoor installation. They are used as high voltage or vacuum leads from transformers of high voltage circuit breakers. The bushing of the present type is made of porcelain, and a metal rod is located inside the product. It is fastened with flanges made of metal joined with a porcelain hat and adhesive sandy composition.
The second type is reassigned for both outdoor and indoor installations. Such devices have intermediate ribs that are located at a short distance from each other. These devices are intended for isolation from live parts of enclosed switchgears. A bushing of this type is used at an operating voltage of 10, 25, 35, 110 kV, and an operating current of 630 to 11,000 A.
Other types of insulators also exist, but they are designed for a specific purpose. Feed-through devices are necessary for isolating the conductive parts of switchgears and for connecting consumers to the overhead power lines with tires. These products are made of materials of increased strength, so that their design is resistant to dynamic current loads.
Benefits of Insulators
The bushing must have a long service life, so it has the following characteristics:
- high resistance to aggressive operating conditions;
- relatively small mass;
- resistance to ultraviolet radiation;
- high strength;
- long service life;
- relatively small overall dimensions.
IP design
IP bushings should have maximum mechanical and electrical strength, therefore, the material from which they are made can be as follows:
- polymer;
- china;
- strained glass.
The insulator is designed so that the breakdown voltage is higher than the overlap voltage. External insulators are constantly influenced by external environmental factors, therefore their surface is ribbed. This is done specifically to improve product performance.
Insulators according to their purpose are divided into walk-through, support and suspended, there are also types of installation for placement in buildings and structures or for outdoor installation.
Passing IP-10 is most often made of porcelain. The design of such an insulator is determined based on the rated voltage and industrial frequency of the network. The product itself consists of a cylindrical porcelain case, on the axes of which ribs are mounted tightly fastened with a cement-sand mortar.
Purpose of bushings
The main purpose of bushing insulators is the insulation of live conductors that pass through the walls and coatings of buildings or structures. Such insulators consist of dielectric porcelain. The housing is made in the form of a cylinder, on the upper part of which there is a current-carrying rod. At the middle level of the casing, metal flanges are installed, which, as mentioned above, are intended for fastening insulators to the surface.
An insulator through passage at an operating voltage of up to 10 kV is made of porcelain, and at an operating voltage of more than 35 kV, the casing of the device is manufactured as a complex insulating structure, which, in turn, consists of a porcelain case, cardboard plates, dielectric paper and transformer oil.
Mounting bushings
During installation, outdoor bushing insulators are inspected for cracks and other defects, since during transportation the surface of the insulators could be damaged. They also examine whether the surface glaze has worn off, which serves to provide additional protection and insulation for the product.
Insulators must be placed on any metal structures for reliable fastening of products, as well as the durability of tires or overhead power lines.
Installation of bushing insulators begins with the placement of a bushing plate, which is fixed to a structure or some kind of reinforcement. Further, the insulators are closed on both sides with cast-iron caps with metal partitions having rectangular openings resembling a railway rail. Their size depends on the size of the fixed tires. At the terminals of the product tires, spacers are installed between the fixed tires.
Marking of bushing
The marking is reassigned in order to highlight all the characteristics of the product. For example, the insulator through passage IP-10 630 7.5 UHL1, where:
- And - an insulator;
- P - checkpoint;
- 10 - normal operating voltage of the product (kV);
- 630 - normal operating current of the product (A);
- 7.5 - destructive force (kN);
- UHL - climatic condition of execution;
- 1 - placement category.
IP breakdown voltage
The breakdown voltage of porcelain PI can be different depending on the thickness of the porcelain layer. Despite this, the design of the insulators is determined by the necessary mechanical strength, the calculated voltage of the overlap and additional measures to remove the corona.
When operating a 10 kV bushing, no measures are taken to remove corona. At rated voltages above 35 kV, measures are taken to install the corona near the rod opposite the flange, just in the place where the greatest tension in the air.
In order to prevent corona, insulators are made without an air cavity around a metal rod installed inside the insulator. During this, the surface of the IP is metallized with the rod. And in order to eliminate the appearance of discharges below the IP, the surface under it is also metallized and additionally grounded.
Conclusion
Probably, everyone has ever seen a transformer, the air lines of which are attached to the IP. These devices are also necessary for connecting wires to fixed installations, since it is impossible to connect high-voltage wires without insulators.